Raise ArgumentError "Cannot infer root key from collection type. Please specify the root or each_serializer option, or render a JSON String" when collection is empty array in >= 10.0.7

[tashirosota]

Expected behavior vs actual behavior

• 【Expected behavior】※ <= version 10.0.6

::ActiveModelSerializers::SerializableResource.new(
  collections, # [] empty array
  each_serializer: CollectionSerializer,
).serializable_hash
=> { collection_types: nil }

• 【Actual behavior】※ >= version 10.0.7

::ActiveModelSerializers::SerializableResource.new(
  collections, # [] empty array
  each_serializer: CollectionSerializer,
).serializable_hash
=> Raise ArgumentError  "Cannot infer root key from collection type. Please specify the root or each_serializer option, or render a JSON String"

Is this breaking change or bug?

Steps to reproduce

(e.g., detailed walkthrough, runnable script, example application)

# >= version 10.0.7
::ActiveModelSerializers::SerializableResource.new(
  collections, # [] empty array
  each_serializer: CollectionSerializer,
).serializable_hash

Environment

ActiveModelSerializers Version (commit ref if not on tag): >= 10.0.7

Output of ruby -e "puts RUBY_DESCRIPTION": ruby 2.6.6p146 && 2.5.1

OS Type & Version: alpine3.12 on docker

Integrated application and version (e.g., Rails, Grape, etc): Rails 5.2.4.4 & 5.1.6

Backtrace

(e.g., provide any applicable backtraces from your application)

• 10.0.7 PR: Fail if collection type cannot be inferred with json adapter (#2210) #2214

Additonal helpful information

(e.g., Gemfile.lock, configurations, PR containing a failing test, git bisect results)

In PR #2214, @mvz said「I'm getting this error on a line that does have :each_serializer specified 😞」. Me too.